The present invention relates to a new and improved method of, and apparatus for, carbonizing or coking fluent carbon-containing material, such as wood, peat, residues, wastes or the like, with the aid of gases in an inclined treatment chamber through which there is moved the material due to the force of gravity from the top towards the bottom while utilizing the flow action of the material upon exceeding the natural angle of repose of the material, whereas gas is conducted from the bottom towards the top in countercurrent flow to the material through the treatment chamber.
From considerable time in the past wood charcoal has been fabricated by "coking" or "carbonizing" or pyrolysis, there occurring a thermal decomposition of the wood molecules under reduction conditions (deficiency in oxygen). Normally the heat needed for pyrolysis or for a combustion process is formed from the combustion of vapors or gaseous, volatile substances, which are formed during the distillation of the raw material. Primitive "furnaces" are formed by wooden heaps or piles which are covered by sand having holes for the inlet of air and the outlet of flue gases and volatile substances. Such furnaces or better stated kilns can only each be used for one charge.
There are also in use actual furnaces formed of metal or refractory stone or bricks, which are suitable for multiple use and operate cyclically. A cycle thus requires a number of days, sometimes weeks.
In order to avoid the numerous limitations with such furnaces which are to be operated in cycles, namely the very low yield, a large amount of manual labor (under very unfavorable working conditions), air polution and so forth, there have been developed continuous devices. The material which is to be carbonized is more or less continually delivered to the furnace and the fabricated charcoal or wood charcoal, after passing through the furnace, is likewise continuously removed. Such type devices are generally complicated, because they usually require mechanical systems for conveying the charge in the form of solids through the furnace under very unfavorable conditions (extremely high temperatures). In this regard attention is directed to U.S. Pat. No. 1,423,527. Consequently, such continuous furnaces are only economical if they are designed for extremely high capacity or high throughput. This leads to the result that a number of projects are only then not realizable because in certain areas there is not available sufficient raw material to be carbonized and adequate for such high capacity.
Prior art inclined chamber furnaces, such as disclosed in British Pat. No. 206,230, U.S. Pat. No. 1,003,702 and U.S. Pat. No. 1,423,527, work with indirect heating, and the combustion occurs in a separate combustion chamber through the walls of which there is heated the treatment chamber. In certain furnaces of this construction the treatment chamber possesses an inclination in the order of magnitude of the natural angle of repose of the material to be carbonized, for instance as taught in U.S. Pat. No. 1,003,702, so that there need not be employed mechanical conveyor means for the material in the treatment chamber. However, the indirect heating requires at least two separate chambers and is not very favorable as concerns the efficiency of the system.
There is also known to the art an inclined chamber furnace with a treatment chamber inclined at the natural angle of repose, wherein a mixture of compressed air and distillation gases is conducted above the material in unidirectional flow with the material and in direct contact with such from the top towards the bottom and then is fed back under the bed of material is countercurrent flow, in order to thus indirectly heat the material from below. In this regard attention is invited to U.S. Pat. No. 3,148,128. This furnace, in principle, possesses the same drawbacks as the just described furnace.
During coking or carbonization there are accomplished the primary method steps:
(a) Drying: during such the water contained in the material charge is vaporized; PA1 (b) Degasification or volatilization: during this step, following drying and as a result of a corresponding temperature rise, the liquids contained in the wood are transformed into volatile gases; PA1 (c) Coking or carbonization: at higher temperatures the molecules of wood or residues, which normally contain carbon, hydrogen, oxygen and, when there are present proteins, also nitrogen, are split or decomposed, and there remain a content of carbon and inorganic constituents (carbon ash) as solids.
The speed of the method steps is dependent essentially upon the temperature according to which the process operates. Higher temperatures mean more rapid coking.